This is going to be the most exciting WWDC for me (I've been an iOS user since September 2010). I can't wait to see what's changed in iOS 7. By the way, don't be surprised if there are drastic changes.
There have always been ideas and prototypes at Apple. Both for hardware and software. When it comes to physical design, there are limitations due to hardware which is a fixed limit. When it comes to software, things can be changed pretty fast if you have the right amount of people who know what they are doing.
Changing the design of iOS will not be a difficult task due to Ives having the final say (he and Jobs had the most power at Apple). No one will tell him no. If he wants iOS to look a certain way then it will.